Generally, in a manufacturing process of a magnetic tape, it is known that defects occur in the magnetic tape due to magnetic liquid of a state mixed with foreign matters such as dust being coated on a supporting body (base tape), not being locally coated because of defects of the supporting body itself, and the like.
Moreover, in a magnetic tape for high-density recording, a servo signal is written by a servo writer and defects also occur in the magnetic tape due to a writing error of the servo signal.
In a portion with such the defects, because data cannot be recorded/reproduced, a magnetic tape including a defect portion needs to be eliminated.
For an eliminating method, there is a following one.
There exists a method that a magnetic tape wound in a pancake, after a servo signal being written by a servo writer, is wound by a winding device on a product reel, so when errors exist inspecting a servo signal writing error of the magnetic tape in winding by the winding device, products together with a reel is scrapped as a product reel with defect portions.
On the other hand, there exists another method that memorizing positions with defects in a pancake in advance, when there exists no defect within a predetermined length in winding on a reel, wind the length as it is, and when there exists a defect, control to wind tape till a portion with the defect on a reject reel and scrap a magnetic tape wound on the reject reel (for example, see pages 3 and 4, and FIG. 1 in Japan patent laid open publication 7-37362).
However, there exists a problem that to scrap tape having defects in a part together with a reel on which hundreds of meters of the tape with the defects in a part are wound results in scrapping a portion of a magnetic tape which can be effectively utilized and there is a considerably large amount of waste.
When a production plan is such a one to cut out a single length of tape from a pancake, the above waste is inevitable, however when cutting out different lengths of tape, there should exist a combination of a cutting-out method with less waste.